The present invention relates generally to gas turbine engines, and, more specifically, to combustors therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Energy is extracted from the gases in turbine stages which power the compressor and a shaft that typically drives a fan in an aircraft turbofan engine application.
A high pressure turbine (HPT) directly follows the combustor and receives the hottest gases therefrom from which energy is initially extracted. A low pressure turbine (LPT) follows the HPT and extracts additional energy from the gases.
In the combustor, fuel and air are mixed and ignited for generating the hot combustion gases. Combustion efficiency is a primary factor in the overall efficiency of the gas turbine engine.
Furthermore, exhaust emissions are also important design factors since government regulations typically limit the amount of undesirable exhaust products, including unburned hydrocarbons UHC, carbon monoxide CO, and nitrogen oxides NOx.
Modern combustor design further addresses combustor durability and life under the extremely hostile operating environment of generating and containing the hot combustion gases. The various combustor complements are subject to considerable heat loads, and must be suitably cooled during operation for suitable life.
Combustors may be operated rich but that increases fuel consumption and undesirable carbon emissions. Combustors may be operated lean to reduce nitrogen oxide emissions, but combustion stability is decreased.
In a dry low emissions (DLE) combustor, the fuel is burned lean which subjects the combustor to possible instability in which large acoustic pressures can drive structural vibrations and increase heat flux into the combustor liners.
Flame flashback in its longitudinal mode is another problem, along with flame blow off in tangential or radial modes.
Combustion instability may be resolved by introducing a flameholder in the combustor to anchor the lean, premixed combustion flame. However, the anchored flame can overheat the flameholder itself and thereby decrease durability and life of the combustor.
These competing design considerations for the combustor require corresponding compromises in design, and further increase the complexity of combustor design.
Accordingly, it is desired to provide a combustor configured for dry low emissions performance with enhanced flame stability.